// Copyright 2010 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_V8_PROFILER_H_
#define V8_V8_PROFILER_H_

#include <vector>
#include "v8.h"  // NOLINT(build/include)

/**
 * Profiler support for the V8 JavaScript engine.
 */
namespace v8 {

class HeapGraphNode;
struct HeapStatsUpdate;

typedef uint32_t SnapshotObjectId;


struct CpuProfileDeoptFrame {
    int script_id;
    size_t position;
};

}  // namespace v8

#ifdef V8_OS_WIN
template class V8_EXPORT std::vector<v8::CpuProfileDeoptFrame>;
#endif

namespace v8 {

struct V8_EXPORT CpuProfileDeoptInfo {
    /** A pointer to a static string owned by v8. */
    const char* deopt_reason;
    std::vector<CpuProfileDeoptFrame> stack;
};

}  // namespace v8

#ifdef V8_OS_WIN
template class V8_EXPORT std::vector<v8::CpuProfileDeoptInfo>;
#endif

namespace v8 {

/**
 * TracingCpuProfiler monitors tracing being enabled/disabled
 * and emits CpuProfile trace events once v8.cpu_profile2 tracing category
 * is enabled. It has no overhead unless the category is enabled.
 */
class V8_EXPORT TracingCpuProfiler {
    public:
        static std::unique_ptr<TracingCpuProfiler> Create(Isolate*);
        virtual ~TracingCpuProfiler() = default;

    protected:
        TracingCpuProfiler() = default;
};

// TickSample captures the information collected for each sample.
struct TickSample {
    // Internal profiling (with --prof + tools/$OS-tick-processor) wants to
    // include the runtime function we're calling. Externally exposed tick
    // samples don't care.
    enum RecordCEntryFrame { kIncludeCEntryFrame, kSkipCEntryFrame };

    TickSample()
        : state(OTHER),
          pc(nullptr),
          external_callback_entry(nullptr),
          frames_count(0),
          has_external_callback(false),
          update_stats(true) {}

    /**
     * Initialize a tick sample from the isolate.
     * \param isolate The isolate.
     * \param state Execution state.
     * \param record_c_entry_frame Include or skip the runtime function.
     * \param update_stats Whether update the sample to the aggregated stats.
     * \param use_simulator_reg_state When set to true and V8 is running under a
     *                                simulator, the method will use the simulator
     *                                register state rather than the one provided
     *                                with |state| argument. Otherwise the method
     *                                will use provided register |state| as is.
     */
    void Init(Isolate* isolate, const v8::RegisterState& state,
              RecordCEntryFrame record_c_entry_frame, bool update_stats,
              bool use_simulator_reg_state = true);
    /**
     * Get a call stack sample from the isolate.
     * \param isolate The isolate.
     * \param state Register state.
     * \param record_c_entry_frame Include or skip the runtime function.
     * \param frames Caller allocated buffer to store stack frames.
     * \param frames_limit Maximum number of frames to capture. The buffer must
     *                     be large enough to hold the number of frames.
     * \param sample_info The sample info is filled up by the function
     *                    provides number of actual captured stack frames and
     *                    the current VM state.
     * \param use_simulator_reg_state When set to true and V8 is running under a
     *                                simulator, the method will use the simulator
     *                                register state rather than the one provided
     *                                with |state| argument. Otherwise the method
     *                                will use provided register |state| as is.
     * \note GetStackSample is thread and signal safe and should only be called
     *                      when the JS thread is paused or interrupted.
     *                      Otherwise the behavior is undefined.
     */
    static bool GetStackSample(Isolate* isolate, v8::RegisterState* state,
                               RecordCEntryFrame record_c_entry_frame,
                               void** frames, size_t frames_limit,
                               v8::SampleInfo* sample_info,
                               bool use_simulator_reg_state = true);
    StateTag state;  // The state of the VM.
    void* pc;        // Instruction pointer.
    union {
        void* tos;  // Top stack value (*sp).
        void* external_callback_entry;
    };
    static const unsigned kMaxFramesCountLog2 = 8;
    static const unsigned kMaxFramesCount = (1 << kMaxFramesCountLog2) - 1;
    void* stack[kMaxFramesCount];                 // Call stack.
unsigned frames_count :
    kMaxFramesCountLog2;  // Number of captured frames.
    bool has_external_callback : 1;
    bool update_stats : 1;  // Whether the sample should update aggregated stats.
};

/**
 * CpuProfileNode represents a node in a call graph.
 */
class V8_EXPORT CpuProfileNode {
    public:
        struct LineTick {
            /** The 1-based number of the source line where the function originates. */
            int line;

            /** The count of samples associated with the source line. */
            unsigned int hit_count;
        };

        /** Returns function name (empty string for anonymous functions.) */
        Local<String> GetFunctionName() const;

        /**
         * Returns function name (empty string for anonymous functions.)
         * The string ownership is *not* passed to the caller. It stays valid until
         * profile is deleted. The function is thread safe.
         */
        const char* GetFunctionNameStr() const;

        /** Returns id of the script where function is located. */
        int GetScriptId() const;

        /** Returns resource name for script from where the function originates. */
        Local<String> GetScriptResourceName() const;

        /**
         * Returns resource name for script from where the function originates.
         * The string ownership is *not* passed to the caller. It stays valid until
         * profile is deleted. The function is thread safe.
         */
        const char* GetScriptResourceNameStr() const;

        /**
         * Returns the number, 1-based, of the line where the function originates.
         * kNoLineNumberInfo if no line number information is available.
         */
        int GetLineNumber() const;

        /**
         * Returns 1-based number of the column where the function originates.
         * kNoColumnNumberInfo if no column number information is available.
         */
        int GetColumnNumber() const;

        /**
         * Returns the number of the function's source lines that collect the samples.
         */
        unsigned int GetHitLineCount() const;

        /** Returns the set of source lines that collect the samples.
         *  The caller allocates buffer and responsible for releasing it.
         *  True if all available entries are copied, otherwise false.
         *  The function copies nothing if buffer is not large enough.
         */
        bool GetLineTicks(LineTick* entries, unsigned int length) const;

        /** Returns bailout reason for the function
          * if the optimization was disabled for it.
          */
        const char* GetBailoutReason() const;

        /**
          * Returns the count of samples where the function was currently executing.
          */
        unsigned GetHitCount() const;

        /** Returns function entry UID. */
        V8_DEPRECATE_SOON(
            "Use GetScriptId, GetLineNumber, and GetColumnNumber instead.",
            unsigned GetCallUid() const);

        /** Returns id of the node. The id is unique within the tree */
        unsigned GetNodeId() const;

        /** Returns child nodes count of the node. */
        int GetChildrenCount() const;

        /** Retrieves a child node by index. */
        const CpuProfileNode* GetChild(int index) const;

        /** Retrieves deopt infos for the node. */
        const std::vector<CpuProfileDeoptInfo>& GetDeoptInfos() const;

        static const int kNoLineNumberInfo = Message::kNoLineNumberInfo;
        static const int kNoColumnNumberInfo = Message::kNoColumnInfo;
};


/**
 * CpuProfile contains a CPU profile in a form of top-down call tree
 * (from main() down to functions that do all the work).
 */
class V8_EXPORT CpuProfile {
    public:
        /** Returns CPU profile title. */
        Local<String> GetTitle() const;

        /** Returns the root node of the top down call tree. */
        const CpuProfileNode* GetTopDownRoot() const;

        /**
         * Returns number of samples recorded. The samples are not recorded unless
         * |record_samples| parameter of CpuProfiler::StartCpuProfiling is true.
         */
        int GetSamplesCount() const;

        /**
         * Returns profile node corresponding to the top frame the sample at
         * the given index.
         */
        const CpuProfileNode* GetSample(int index) const;

        /**
         * Returns the timestamp of the sample. The timestamp is the number of
         * microseconds since some unspecified starting point.
         * The point is equal to the starting point used by GetStartTime.
         */
        int64_t GetSampleTimestamp(int index) const;

        /**
         * Returns time when the profile recording was started (in microseconds)
         * since some unspecified starting point.
         */
        int64_t GetStartTime() const;

        /**
         * Returns time when the profile recording was stopped (in microseconds)
         * since some unspecified starting point.
         * The point is equal to the starting point used by GetStartTime.
         */
        int64_t GetEndTime() const;

        /**
         * Deletes the profile and removes it from CpuProfiler's list.
         * All pointers to nodes previously returned become invalid.
         */
        void Delete();
};

/**
 * Interface for controlling CPU profiling. Instance of the
 * profiler can be created using v8::CpuProfiler::New method.
 */
class V8_EXPORT CpuProfiler {
    public:
        /**
         * Creates a new CPU profiler for the |isolate|. The isolate must be
         * initialized. The profiler object must be disposed after use by calling
         * |Dispose| method.
         */
        static CpuProfiler* New(Isolate* isolate);

        /**
         * Disposes the CPU profiler object.
         */
        void Dispose();

        /**
         * Changes default CPU profiler sampling interval to the specified number
         * of microseconds. Default interval is 1000us. This method must be called
         * when there are no profiles being recorded.
         */
        void SetSamplingInterval(int us);

        /**
         * Starts collecting CPU profile. Title may be an empty string. It
         * is allowed to have several profiles being collected at
         * once. Attempts to start collecting several profiles with the same
         * title are silently ignored. While collecting a profile, functions
         * from all security contexts are included in it. The token-based
         * filtering is only performed when querying for a profile.
         *
         * |record_samples| parameter controls whether individual samples should
         * be recorded in addition to the aggregated tree.
         */
        void StartProfiling(Local<String> title, bool record_samples = false);

        /**
         * Stops collecting CPU profile with a given title and returns it.
         * If the title given is empty, finishes the last profile started.
         */
        CpuProfile* StopProfiling(Local<String> title);

        /**
         * Force collection of a sample. Must be called on the VM thread.
         * Recording the forced sample does not contribute to the aggregated
         * profile statistics.
         */
        void CollectSample();

        /**
         * Tells the profiler whether the embedder is idle.
         */
        void SetIdle(bool is_idle);

    private:
        CpuProfiler();
        ~CpuProfiler();
        CpuProfiler(const CpuProfiler&);
        CpuProfiler& operator=(const CpuProfiler&);
};


/**
 * HeapSnapshotEdge represents a directed connection between heap
 * graph nodes: from retainers to retained nodes.
 */
class V8_EXPORT HeapGraphEdge {
    public:
        enum Type {
            kContextVariable = 0,  // A variable from a function context.
            kElement = 1,          // An element of an array.
            kProperty = 2,         // A named object property.
            kInternal = 3,         // A link that can't be accessed from JS,
            // thus, its name isn't a real property name
            // (e.g. parts of a ConsString).
            kHidden = 4,           // A link that is needed for proper sizes
            // calculation, but may be hidden from user.
            kShortcut = 5,         // A link that must not be followed during
            // sizes calculation.
            kWeak = 6              // A weak reference (ignored by the GC).
        };

        /** Returns edge type (see HeapGraphEdge::Type). */
        Type GetType() const;

        /**
         * Returns edge name. This can be a variable name, an element index, or
         * a property name.
         */
        Local<Value> GetName() const;

        /** Returns origin node. */
        const HeapGraphNode* GetFromNode() const;

        /** Returns destination node. */
        const HeapGraphNode* GetToNode() const;
};


/**
 * HeapGraphNode represents a node in a heap graph.
 */
class V8_EXPORT HeapGraphNode {
    public:
        enum Type {
            kHidden = 0,         // Hidden node, may be filtered when shown to user.
            kArray = 1,          // An array of elements.
            kString = 2,         // A string.
            kObject = 3,         // A JS object (except for arrays and strings).
            kCode = 4,           // Compiled code.
            kClosure = 5,        // Function closure.
            kRegExp = 6,         // RegExp.
            kHeapNumber = 7,     // Number stored in the heap.
            kNative = 8,         // Native object (not from V8 heap).
            kSynthetic = 9,      // Synthetic object, usualy used for grouping
            // snapshot items together.
            kConsString = 10,    // Concatenated string. A pair of pointers to strings.
            kSlicedString = 11,  // Sliced string. A fragment of another string.
            kSymbol = 12,        // A Symbol (ES6).
            kSimdValue = 13      // A SIMD value stored in the heap (Proposed ES7).
        };

        /** Returns node type (see HeapGraphNode::Type). */
        Type GetType() const;

        /**
         * Returns node name. Depending on node's type this can be the name
         * of the constructor (for objects), the name of the function (for
         * closures), string value, or an empty string (for compiled code).
         */
        Local<String> GetName() const;

        /**
         * Returns node id. For the same heap object, the id remains the same
         * across all snapshots.
         */
        SnapshotObjectId GetId() const;

        /** Returns node's own size, in bytes. */
        size_t GetShallowSize() const;

        /** Returns child nodes count of the node. */
        int GetChildrenCount() const;

        /** Retrieves a child by index. */
        const HeapGraphEdge* GetChild(int index) const;
};


/**
 * An interface for exporting data from V8, using "push" model.
 */
class V8_EXPORT OutputStream {  // NOLINT
    public:
        enum WriteResult {
            kContinue = 0,
            kAbort = 1
        };
        virtual ~OutputStream() {}
        /** Notify about the end of stream. */
        virtual void EndOfStream() = 0;
        /** Get preferred output chunk size. Called only once. */
        virtual int GetChunkSize() {
            return 1024;
        }
        /**
         * Writes the next chunk of snapshot data into the stream. Writing
         * can be stopped by returning kAbort as function result. EndOfStream
         * will not be called in case writing was aborted.
         */
        virtual WriteResult WriteAsciiChunk(char* data, int size) = 0;
        /**
         * Writes the next chunk of heap stats data into the stream. Writing
         * can be stopped by returning kAbort as function result. EndOfStream
         * will not be called in case writing was aborted.
         */
        virtual WriteResult WriteHeapStatsChunk(HeapStatsUpdate* data, int count) {
            return kAbort;
        }
};


/**
 * HeapSnapshots record the state of the JS heap at some moment.
 */
class V8_EXPORT HeapSnapshot {
    public:
        enum SerializationFormat {
            kJSON = 0  // See format description near 'Serialize' method.
        };

        /** Returns the root node of the heap graph. */
        const HeapGraphNode* GetRoot() const;

        /** Returns a node by its id. */
        const HeapGraphNode* GetNodeById(SnapshotObjectId id) const;

        /** Returns total nodes count in the snapshot. */
        int GetNodesCount() const;

        /** Returns a node by index. */
        const HeapGraphNode* GetNode(int index) const;

        /** Returns a max seen JS object Id. */
        SnapshotObjectId GetMaxSnapshotJSObjectId() const;

        /**
         * Deletes the snapshot and removes it from HeapProfiler's list.
         * All pointers to nodes, edges and paths previously returned become
         * invalid.
         */
        void Delete();

        /**
         * Prepare a serialized representation of the snapshot. The result
         * is written into the stream provided in chunks of specified size.
         * The total length of the serialized snapshot is unknown in
         * advance, it can be roughly equal to JS heap size (that means,
         * it can be really big - tens of megabytes).
         *
         * For the JSON format, heap contents are represented as an object
         * with the following structure:
         *
         *  {
         *    snapshot: {
         *      title: "...",
         *      uid: nnn,
         *      meta: { meta-info },
         *      node_count: nnn,
         *      edge_count: nnn
         *    },
         *    nodes: [nodes array],
         *    edges: [edges array],
         *    strings: [strings array]
         *  }
         *
         * Nodes reference strings, other nodes, and edges by their indexes
         * in corresponding arrays.
         */
        void Serialize(OutputStream* stream,
                       SerializationFormat format = kJSON) const;
};


/**
 * An interface for reporting progress and controlling long-running
 * activities.
 */
class V8_EXPORT ActivityControl {  // NOLINT
    public:
        enum ControlOption {
            kContinue = 0,
            kAbort = 1
        };
        virtual ~ActivityControl() {}
        /**
         * Notify about current progress. The activity can be stopped by
         * returning kAbort as the callback result.
         */
        virtual ControlOption ReportProgressValue(int done, int total) = 0;
};


/**
 * AllocationProfile is a sampled profile of allocations done by the program.
 * This is structured as a call-graph.
 */
class V8_EXPORT AllocationProfile {
    public:
        struct Allocation {
            /**
             * Size of the sampled allocation object.
             */
            size_t size;

            /**
             * The number of objects of such size that were sampled.
             */
            unsigned int count;
        };

        /**
         * Represents a node in the call-graph.
         */
        struct Node {
            /**
             * Name of the function. May be empty for anonymous functions or if the
             * script corresponding to this function has been unloaded.
             */
            Local<String> name;

            /**
             * Name of the script containing the function. May be empty if the script
             * name is not available, or if the script has been unloaded.
             */
            Local<String> script_name;

            /**
             * id of the script where the function is located. May be equal to
             * v8::UnboundScript::kNoScriptId in cases where the script doesn't exist.
             */
            int script_id;

            /**
             * Start position of the function in the script.
             */
            int start_position;

            /**
             * 1-indexed line number where the function starts. May be
             * kNoLineNumberInfo if no line number information is available.
             */
            int line_number;

            /**
             * 1-indexed column number where the function starts. May be
             * kNoColumnNumberInfo if no line number information is available.
             */
            int column_number;

            /**
             * List of callees called from this node for which we have sampled
             * allocations. The lifetime of the children is scoped to the containing
             * AllocationProfile.
             */
            std::vector<Node*> children;

            /**
             * List of self allocations done by this node in the call-graph.
             */
            std::vector<Allocation> allocations;
        };

        /**
         * Returns the root node of the call-graph. The root node corresponds to an
         * empty JS call-stack. The lifetime of the returned Node* is scoped to the
         * containing AllocationProfile.
         */
        virtual Node* GetRootNode() = 0;

        virtual ~AllocationProfile() {}

        static const int kNoLineNumberInfo = Message::kNoLineNumberInfo;
        static const int kNoColumnNumberInfo = Message::kNoColumnInfo;
};


/**
 * Interface for controlling heap profiling. Instance of the
 * profiler can be retrieved using v8::Isolate::GetHeapProfiler.
 */
class V8_EXPORT HeapProfiler {
    public:
        enum SamplingFlags {
            kSamplingNoFlags = 0,
            kSamplingForceGC = 1 << 0,
        };

        /**
         * Callback function invoked for obtaining RetainedObjectInfo for
         * the given JavaScript wrapper object. It is prohibited to enter V8
         * while the callback is running: only getters on the handle and
         * GetPointerFromInternalField on the objects are allowed.
         */
        typedef RetainedObjectInfo* (*WrapperInfoCallback)(uint16_t class_id,
                Local<Value> wrapper);

        /** Returns the number of snapshots taken. */
        int GetSnapshotCount();

        /** Returns a snapshot by index. */
        const HeapSnapshot* GetHeapSnapshot(int index);

        /**
         * Returns SnapshotObjectId for a heap object referenced by |value| if
         * it has been seen by the heap profiler, kUnknownObjectId otherwise.
         */
        SnapshotObjectId GetObjectId(Local<Value> value);

        /**
         * Returns heap object with given SnapshotObjectId if the object is alive,
         * otherwise empty handle is returned.
         */
        Local<Value> FindObjectById(SnapshotObjectId id);

        /**
         * Clears internal map from SnapshotObjectId to heap object. The new objects
         * will not be added into it unless a heap snapshot is taken or heap object
         * tracking is kicked off.
         */
        void ClearObjectIds();

        /**
         * A constant for invalid SnapshotObjectId. GetSnapshotObjectId will return
         * it in case heap profiler cannot find id  for the object passed as
         * parameter. HeapSnapshot::GetNodeById will always return NULL for such id.
         */
        static const SnapshotObjectId kUnknownObjectId = 0;

        /**
         * Callback interface for retrieving user friendly names of global objects.
         */
        class ObjectNameResolver {
            public:
                /**
                 * Returns name to be used in the heap snapshot for given node. Returned
                 * string must stay alive until snapshot collection is completed.
                 */
                virtual const char* GetName(Local<Object> object) = 0;

            protected:
                virtual ~ObjectNameResolver() {}
        };

        /**
         * Takes a heap snapshot and returns it.
         */
        const HeapSnapshot* TakeHeapSnapshot(
            ActivityControl* control = NULL,
            ObjectNameResolver* global_object_name_resolver = NULL);

        /**
         * Starts tracking of heap objects population statistics. After calling
         * this method, all heap objects relocations done by the garbage collector
         * are being registered.
         *
         * |track_allocations| parameter controls whether stack trace of each
         * allocation in the heap will be recorded and reported as part of
         * HeapSnapshot.
         */
        void StartTrackingHeapObjects(bool track_allocations = false);

        /**
         * Adds a new time interval entry to the aggregated statistics array. The
         * time interval entry contains information on the current heap objects
         * population size. The method also updates aggregated statistics and
         * reports updates for all previous time intervals via the OutputStream
         * object. Updates on each time interval are provided as a stream of the
         * HeapStatsUpdate structure instances.
         * If |timestamp_us| is supplied, timestamp of the new entry will be written
         * into it. The return value of the function is the last seen heap object Id.
         *
         * StartTrackingHeapObjects must be called before the first call to this
         * method.
         */
        SnapshotObjectId GetHeapStats(OutputStream* stream,
                                      int64_t* timestamp_us = NULL);

        /**
         * Stops tracking of heap objects population statistics, cleans up all
         * collected data. StartHeapObjectsTracking must be called again prior to
         * calling GetHeapStats next time.
         */
        void StopTrackingHeapObjects();

        /**
         * Starts gathering a sampling heap profile. A sampling heap profile is
         * similar to tcmalloc's heap profiler and Go's mprof. It samples object
         * allocations and builds an online 'sampling' heap profile. At any point in
         * time, this profile is expected to be a representative sample of objects
         * currently live in the system. Each sampled allocation includes the stack
         * trace at the time of allocation, which makes this really useful for memory
         * leak detection.
         *
         * This mechanism is intended to be cheap enough that it can be used in
         * production with minimal performance overhead.
         *
         * Allocations are sampled using a randomized Poisson process. On average, one
         * allocation will be sampled every |sample_interval| bytes allocated. The
         * |stack_depth| parameter controls the maximum number of stack frames to be
         * captured on each allocation.
         *
         * NOTE: This is a proof-of-concept at this point. Right now we only sample
         * newspace allocations. Support for paged space allocation (e.g. pre-tenured
         * objects, large objects, code objects, etc.) and native allocations
         * doesn't exist yet, but is anticipated in the future.
         *
         * Objects allocated before the sampling is started will not be included in
         * the profile.
         *
         * Returns false if a sampling heap profiler is already running.
         */
        bool StartSamplingHeapProfiler(uint64_t sample_interval = 512 * 1024,
                                       int stack_depth = 16,
                                       SamplingFlags flags = kSamplingNoFlags);

        /**
         * Stops the sampling heap profile and discards the current profile.
         */
        void StopSamplingHeapProfiler();

        /**
         * Returns the sampled profile of allocations allocated (and still live) since
         * StartSamplingHeapProfiler was called. The ownership of the pointer is
         * transfered to the caller. Returns nullptr if sampling heap profiler is not
         * active.
         */
        AllocationProfile* GetAllocationProfile();

        /**
         * Deletes all snapshots taken. All previously returned pointers to
         * snapshots and their contents become invalid after this call.
         */
        void DeleteAllHeapSnapshots();

        /** Binds a callback to embedder's class ID. */
        void SetWrapperClassInfoProvider(
            uint16_t class_id,
            WrapperInfoCallback callback);

        /**
         * Default value of persistent handle class ID. Must not be used to
         * define a class. Can be used to reset a class of a persistent
         * handle.
         */
        static const uint16_t kPersistentHandleNoClassId = 0;

        /** Returns memory used for profiler internal data and snapshots. */
        size_t GetProfilerMemorySize();

        /**
         * Sets a RetainedObjectInfo for an object group (see V8::SetObjectGroupId).
         */
        void SetRetainedObjectInfo(UniqueId id, RetainedObjectInfo* info);

    private:
        HeapProfiler();
        ~HeapProfiler();
        HeapProfiler(const HeapProfiler&);
        HeapProfiler& operator=(const HeapProfiler&);
};

/**
 * Interface for providing information about embedder's objects
 * held by global handles. This information is reported in two ways:
 *
 *  1. When calling AddObjectGroup, an embedder may pass
 *     RetainedObjectInfo instance describing the group.  To collect
 *     this information while taking a heap snapshot, V8 calls GC
 *     prologue and epilogue callbacks.
 *
 *  2. When a heap snapshot is collected, V8 additionally
 *     requests RetainedObjectInfos for persistent handles that
 *     were not previously reported via AddObjectGroup.
 *
 * Thus, if an embedder wants to provide information about native
 * objects for heap snapshots, it can do it in a GC prologue
 * handler, and / or by assigning wrapper class ids in the following way:
 *
 *  1. Bind a callback to class id by calling SetWrapperClassInfoProvider.
 *  2. Call SetWrapperClassId on certain persistent handles.
 *
 * V8 takes ownership of RetainedObjectInfo instances passed to it and
 * keeps them alive only during snapshot collection. Afterwards, they
 * are freed by calling the Dispose class function.
 */
class V8_EXPORT RetainedObjectInfo {  // NOLINT
    public:
        /** Called by V8 when it no longer needs an instance. */
        virtual void Dispose() = 0;

        /** Returns whether two instances are equivalent. */
        virtual bool IsEquivalent(RetainedObjectInfo* other) = 0;

        /**
         * Returns hash value for the instance. Equivalent instances
         * must have the same hash value.
         */
        virtual intptr_t GetHash() = 0;

        /**
         * Returns human-readable label. It must be a null-terminated UTF-8
         * encoded string. V8 copies its contents during a call to GetLabel.
         */
        virtual const char* GetLabel() = 0;

        /**
         * Returns human-readable group label. It must be a null-terminated UTF-8
         * encoded string. V8 copies its contents during a call to GetGroupLabel.
         * Heap snapshot generator will collect all the group names, create
         * top level entries with these names and attach the objects to the
         * corresponding top level group objects. There is a default
         * implementation which is required because embedders don't have their
         * own implementation yet.
         */
        virtual const char* GetGroupLabel() {
            return GetLabel();
        }

        /**
         * Returns element count in case if a global handle retains
         * a subgraph by holding one of its nodes.
         */
        virtual intptr_t GetElementCount() {
            return -1;
        }

        /** Returns embedder's object size in bytes. */
        virtual intptr_t GetSizeInBytes() {
            return -1;
        }

    protected:
        RetainedObjectInfo() {}
        virtual ~RetainedObjectInfo() {}

    private:
        RetainedObjectInfo(const RetainedObjectInfo&);
        RetainedObjectInfo& operator=(const RetainedObjectInfo&);
};


/**
 * A struct for exporting HeapStats data from V8, using "push" model.
 * See HeapProfiler::GetHeapStats.
 */
struct HeapStatsUpdate {
    HeapStatsUpdate(uint32_t index, uint32_t count, uint32_t size)
        : index(index), count(count), size(size) { }
    uint32_t index;  // Index of the time interval that was changed.
    uint32_t count;  // New value of count field for the interval with this index.
    uint32_t size;  // New value of size field for the interval with this index.
};


}  // namespace v8


#endif  // V8_V8_PROFILER_H_
